Abstract: An apparatus is provided for programmably silencing a telephone ringer for one or more predetermined periods of time on a daily basis. In accordance with the time set by a user, the apparatus places the telephone ringer under the control of the data stored in the read only memory and the random access memory of the central processing unit, whereby the ringer can be automatically set at predetermined sounding condition.

Abstract: A hot-line device for telephone sets includes a logic AND gate circuit serving as a central unit with its output to be electrically connected to a control circuit through the keyboard of a telephone set, and its inputs respectively coupled with a hot-line triggering circuit, a dial-tone detection circuit and a ringing detection and delay circuit separately disposed in the telephone set for automatically effecting dialing operation during an emergency situation. Alternatively, the logic AND gate circuit can be replaced with a microprocessor for performing automatic dialing operation through a predetermined program.

Abstract: A switching control apparatus for intercom-telephone sets includes a switching control circuit and a surge protection circuit electrically coupled with a talking circuit for increasing the reliability of the intercom-telephone operation, reducing the cost of manufacturing the product and protecting the intercom-telephone sets against high voltage surges which may damage the intercom-telephone sets during electrical storms.

Abstract: An automatic telephone silencer and volume controller having a microprocessor for storing time and volume information and for timely controlling the sound characteristics of a telephone ringer in accordance with the time and volume information stored. The time and volume information may be entered into the microprocessor by a suitable keyboard. Each time entry has associated with it a volume entry so that the telephone will ring at the prescribed volume from that time until the time denoted by the next time entry.